A radioactive sludge contaminated by radioactive substance (called merely “sludge” hereinafter) composed of an ion exchange resin or filtration auxiliary agent and the like, which may be generated according to the operation (i.e., running) of a nuclear power plant, is stored for a certain predetermined time in a sludge storage tank together with supernatant solution for attenuating radiation, thereafter, taken out from the sludge storage tank, and then, transferred to and treated at a processing section.
Further, the supernatant solution is generated by a reason such that when the sludge is transferred to the storage tank, it is impossible to transfer the sludge on its own, so that it is necessary to make the sludge as sludge solution (liquid state) having fluidity by being mixed with water or like. When the thus formed sludge solution is transferred to the storage tank, the sludge is precipitated downward in the storage tank, and hence, the supernatant solution is generated above the precipitated sludge.
It is required for such sludge storage tank to have high reliability, and accordingly, the sludge storage tank is periodically inspected to inspect leakage or like of the supernatant, and repaired as occasion demands. In order to carry out the inspection of the sludge storage tank, it is necessary to empty the sludge storage tank, which requires for the stored sludge to be transferred or delivered into another tank. However, it is an essential requirement that such transferring working should be performed under the condition of most-reduced exposure of radiation to workers.
One example of a radioactive sludge transfer apparatus for solving the above inevitable problem is disclosed in Patent Document 1 (Japanese Patent Publication No. 4356728). Hereunder, this radioactive sludge transfer apparatus disclosed in the above publication will be mentioned as “conventional transfer system” and explained with reference to a drawing.
FIG. 11 is a schematic diagram showing a structure of the conventional transfer system.
With reference to FIG. 11, reference character T1 denotes a sludge storage tank in which sludge 31 is stored, reference character T2 denotes a transfer tank, as another tank, into which the sludge 31 stored in the sludge storage tank T1 is transferred, reference numeral 32 is supernatant solution of the sludge 31, and reference numeral 33 is an air-blowing device including an air supply source 34, an air pipe 35 and an air nozzle 36. The air-blowing device 33 injects air to the supernatant solution of the sludge 31 stored in the sludge storage tank T1 to thereby locally stir the supernatant solution 32, thus generating a sludge solution 37 having fluidity.
Reference character P1 denotes a sludge transfer pump, reference character P2 is a supernatant solution return pump disposed inside the transfer tank T2, reference numeral 38 is a sludge solution transfer path connecting the sludge transfer pump P1 and the transfer tank T2, reference numeral 39 is a supernatant solution transfer path connected to the supernatant solution return pump P2, and reference numeral 40 is a supernatant solution jetting device connecting to the supernatant solution transfer path 39. The supernatant solution jetting device 40 acts to spray or jet the supernatant solution 32, as highly pressurized water jet, from the supernatant solution transfer path 39 toward the sludge 31 stored in the sludge storage tank T1 through a supernatant solution jetting nozzle 42 mounted to a supernatant solution pipe 41.
The above-mentioned air pipe 35, the sludge solution transfer path 38, the supernatant solution transfer path 39 and the supernatant solution pipe 41 are set into the sludge storage tank T1 or the transfer tank T2 through inspection holes 43 which are shielded by radiation shielding means 44, respectively.
Further, reference numeral 45 denotes a monitoring camera set to the sludge storage tank T1 so as to monitor the condition such as sludge solution forming state or process inside the sludge storage tank T1. Reference numeral 46 is a monitoring camera set inside the transfer tank T2 so as to monitor the condition such as supernatant solution forming state or process inside the transfer tank T2. Reference numeral 47 is a control device that controls, in accordance with image information from the monitoring cameras 45 and 46, a series of sludge transferring operations by operating valves B1 to B4 mounted to the air-blowing device 33, the supernatant solution jetting device 40, the sludge solution transfer path 38 and the supernatant solution transfer path 39.
According to the conventional transfer system, the sludge 31 stored in the sludge storage tank T1 is transferred to the transfer tank T2 in a manner mentioned hereunder.
First, air is blown into the supernatant solution in the sludge storage tank T1 by means of the air-blowing device 33 to thereby locally stir the supernatant solution. According to this operation, the sludge 31 stored in the sludge storage tank T1 is crushed, and a sludge solution 37 having fluidity is thereby formed on the sludge 31.
When the sludge solution 37 is formed by the manner mentioned above, the sludge solution 37 is sucked by the sludge transfer pump P1 and then transferred to the transfer tank T2 through the sludge solution transfer path 38. The sludge solution 37 transferred into the transfer tank T2 is separated into the sludge 31 and the supernatant solution 32 according to the time elapsed.
According to the operation mentioned above, when the supernatant solution 32 is stored in the inside of the transfer tank T2, the supernatant solution 32 is sucked by the supernatant solution return pump P2 and transfer the supernatant solution 32 to the supernatant solution jetting device 40 through the supernatant solution transfer path 39. The supernatant solution jetting device 40 acts to jet or spray the supernatant solution 32 onto the sludge 31 stored in the sludge storage tank T1 through the supernatant solution jetting nozzle 42 via the supernatant solution pipe 41. Thus, the sludge 31 is crushed and the sludge solution 37 is then formed.
Thereafter, the sludge solution 37 in the sludge storage tank T1 is sucked again by the sludge transfer pump P1 and then transferred to the transfer tank T2 through the sludge transfer path 38. Then, the supernatant solution in the transfer tank T2 is jetted or blown to the sludge 31 stored in the sludge storage tank T1.
By repeating the above operation or working, the sludge 31 stored in the sludge storage tank T1 can be transferred to the transfer tank T2.